But a European office of a US company is able to do business with the Middle Eastern country, provided an entire technology and project is developed by that office.

“If as much as one email passes Europe and the US headquarters, that’s enough for an investment to become technically in breach of sanctions,” the source continued.

These nightmarishly difficult restrictions come as Iran attempts to build no less than seven grassroots refineries in a attempt to rectify deficits in fuel products – one each at Shahriar, Anahita, Caspian, Khuzestan and Pars and two at Hormuz.

Numerous other expansions at existing refineries are being planned with the likely investment costs running into many billions of Euros.

Scepticism is easy following big delays in previous natural grass processing, refining and petrochemical investments due to sanctions that limit financing and technology and skills transfer.

Doubts have also been raised over the level of investment in maintaining output from the oil fields that would supply this new refinery capacity.